Extract out UserDataRepository.UserData

As a preparation to reduce redundant usages of IMMS#getUserData(),
this CL extracts out UserDataRepository.UserData so that we can refer
to UserData a bit more easily.

This is a mechanical code refactoring. There must be no behavior
change.

Bug: 353307830
Test: presubmit
Flag: EXEMPT refactor
Change-Id: Ib2dcb59c9de8ea1fd428dd2fe3ee87d954cc294a